In order to ensure a secure and efficient operation of a system, it is desirable to be able to discover impaired performance ability in the high pressure pump early, in order to be able to take suitable measures for the pump to function optimally again, or in order to replace the pump. Herein, limited performance ability of the high pressure pump may be due to the occurrence of a leak in one or several of the pump elements between the inlet valve and the pump chamber's connecting opening to the low pressure part, e.g. because of a somewhat damaged valve, or leakage between the piston and pump chamber wall because of wear particles getting caught in the fuel and damaging the wall.
U.S. Pat. No. 7,431,018 describes a method for detecting faults in a high pressure pump by measuring the fuel pressure in the area of the accumulator tank and comparing this with reference values. This is done with the help of a pressure regulator and pressure fault sensor, and the method described therein consists of a relatively blunt instrument for function control of a high pressure pump, and is more focused on discovering larger faults in the function of the same.